1. Field of the Invention
This invention relates to detection of objects ahead of a highway vehicle, detection of objects in lanes adjacent to and immediately behind the vehicle, and to detection of boundaries of the lane occupied by the vehicle.
2. Prior Art
Heretofore currently available commercial vehicles sensor systems typically performed only a single function. On the other hand, radar object sensors capable of three dimensional (range, azimuth, and elevation) multiple object detection have been available for some time for military applications. Additionally, forward looking radar sensors have been deployed for automotive applications, primarily for adaptive cruise control systems. These systems are typically capable only of two dimensional (range and azimuth) detection. Two dimensional sensors are not adequately reliable for long distance determination of a hazard. Without elevation information of an object far ahead, it is difficult to reliably determine whether it is a harmless overhead object (bridge or sign) or a hazard (disabled vehicle in the same lane). Therefore, no reliable forward looking collision warning sensor system has been commercialized for use by the general public.
The current art of automotive forward looking sensors is based on a single sensor mounted at the front center of the vehicle. Because the beam angle is relatively narrow (typically 3-10 degrees) there are azimuth blind zones at short range forward of the vehicle on the left and right side of the beam. These blind zones prevent detection of vehicles that cut in close to the host vehicle (5-50 meters) or any obstacle that may present an immediate threat of collision.
Radar distance/velocity detectors for vehicular application are disclosed in U.S. Pat. Nos. 5,677,695; 5,839,534; 5,436,835; 5,341,144. These patents give considerable detail regarding object range measurement but no consideration to object location in either azimuth angle or elevation angle.
An automotive vehicle tracking radar is described in U.S. Reissue Pat. No. RE 36,819 in which a two-lobe monopulse antenna is used for determining angle of multiple targets in the antenna field-of-view.
Another vehicle collision avoidance system is described in U.S. Pat. No. 5,091,726. This system includes forward and rearward beams that provide range and velocity information. This system does include means for tracking vehicles in azimuth or elevation angle direction.
Various inventors have described means for achieving one-dimensional beam scanning of an antenna that is fixed. For example, U.S. Pat. No. 5,752,596 sets out an application of beam scanning for automotive forward looking radar in the azimuth plane. No means for scanning in the elevation plane is described.
A system that includes a safe stopping distance detector and related antenna for vehicles is described in U.S. Pat. No. 5,278,692. This system employs a patch array antenna to cover a field-of-view ahead of a vehicle. While consideration is given to separating the patch array into two sections for detection of the object azimuth angle, no mention of elevation angle detection is given.
Lastly, a vehicle detection and collision avoidance apparatus described in U.S. Pat. No. 4,626,850 uses an acoustic transducer (for obstacle ranging) and describes mechanically scanning of the acoustic transducer to obtain azimuth angle information. Again, there is no consideration for detecting the elevation angle of the obstacle.